The present invention relates generally to microturbine power generating systems. More specifically, the present invention relates to a microturbine power generating system including a combustor and a gas compressor for supplying gaseous fuel to the combustor.
A microturbine power generation unit can operate on liquid fuel or gaseous fuel. Natural gas is a desirable gaseous fuel because it is relatively inexpensive and readily available. It can be supplied by tapping into an existing natural gas line. For microturbine power generation units located in oil fields, the natural gas is free. Natural gas normally be flared at well heads may instead be used to power the microturbine power generation units.
A microturbine power generation unit that is adapted to run on gaseous fuel might include a combustor, a motor-driven gas compressor, a control for operating the gas compressor at a constant speed to provide a maximum flow rate of gas, and a fuel control valve assembly for accurately regulating fuel flow to the combustor. The fuel control valve assembly might include a flow control valve, a pressure regulator, and a shutoff valve.
There are certain drawbacks associated with adapting a microturbine power generation unit in such a manner. One drawback is that operating the gas compressor at constant speed can be inefficient. The compressor provides compressed gas at a maximum flow rate even though the maximum flow rate might not be needed (e.g., when the microturbine generation unit output varies). Compressed gas that is not needed is returned to an inlet of the compressor. However, energy is wasted on compressing the gas that is returned to the compressor inlet.
Pressure variations in the supply line can also reduce the efficiency of the gas compressor operating at constant speed. Pressure variations might increase the flow rate above what is needed. Consequently, compressed gas that is not needed is returned to the compressor inlet. More energy is wasted.
Another drawback is the addition of an inverter for supplying an excitation current to the compressor motor. The inverter can be relatively expensive.
Yet another drawback is that the fuel control valve assembly can be complex and relatively expensive.